Polymeric resins are commonly employed in a variety of different uses. For example, polymeric resins may be employed as support resins for waterborne emulsions. Typical surfactant-based emulsion polymerization products generally do not have the rheology properties desired for graphic arts and industrial coatings applications (i.e. film build, flow and leveling, and stability). It is, therefore, a common practice to add to the emulsion polymerization a low molecular weight water-soluble or alkaline-soluble polymer (also referred to in the art as a resin) in place of, or in addition to, a surfactant in order to improve the stability and rheology properties of the emulsion. Such improved stability generally results from adsorption of the resin on the surface of the polymer particles.
Supported emulsions are commonly employed in paints, clear coatings, floor finishes, leather treatments, cement formulations, functional paper coatings, and graphic art applications. The latter encompasses pigmented (ink) and non-pigmented (overprints and functional coatings) formulations. A support emulsion is comprised of two polymers, one that represents the support resin and a second polymer that is dispersed into the support. The second polymer may be dispersed through agitation or actually be polymerized in the presence of the support resin. Supported emulsions add stability while enhancing the flow characteristics of the formulation (thereby resulting in higher gloss and clarity).
Traditional processes for producing polymer support resins are well known (see generally U.S. Pat. Nos. 4,839,413 and 5,216,064, which are hereby incorporated by reference). Commonly a solution polymerization reaction is employed wherein styrenic monomer and acrylic acid is mixed with a hydrocarbon solvent, a polymerization initiator, and a chain transfer agent. Upon completion of the reaction, the solution is stripped of the solvent to yield the acrylic polymer. The polymer is then available for use as a support resin when dissolved in an alkaline water solution. However, major problems exist with such traditional methods of producing support resins. For example, these methods require the use of environmentally adverse hydrocarbon solvents. Moreover, as these solvents are not usable or desirable in water-based coatings, inks or overprint formulations, the solvents must be stripped from the resulting acrylic polymers (thereby causing a yield loss). This stripping step also adds expense to the process due to both the loss of yield and the energy consumed in performing the stripping. Also, these methods must utilize chain transfer agents to regulate the molecular weight of the resulting support resin.
A number of these problems were addressed via the development of rosin-fatty acid vinylic polymer compositions suitable for employment as support resins in emulsion compositions for coating formulations (see generally U.S. Pat. Nos. 6,429,247 and 6,437,033 B1 which are hereby incorporated by reference). However, it was found that some coatings formulated with these support resins tended to exhibit a decreased adhesion and chemical resistance when used on certain substrates, particularly certain metals and alkyd coatings.
Although water-based coatings and inks are comprised of various components, the emulsion polymer is principally responsible for adhesion to the substrate. Adhesion is a quantitative description of the work of detachment between two phases under conditions of failure.
In the present invention, rosin-fatty acid ester vinylic polymer compositions used as support resins for emulsion polymerization are produced preferably in bulk condition, thereby eliminating the costly stripping process for resin production. In addition, the resin polymerization can be performed at a higher temperature than traditional solution polymerization reactions. Moreover, as the present invention employs a lower amount of free radical initiator and little or no chain transfer agent, the resulting resins can be produced at a reduced cost (and unpleasant odors commonly associated with chain transfer agents can be avoided).
Alkyds generally are formed by the esterification polymerization of polyols and polybasic acid. The reaction mixture may also include monobasic acids, fatty acids and the like.
Due to their desired physical properties and low material costs, solvent-based alkyds have long been widely used as ingredients in coating compositions for various materials. For example, films resulting from aqueous alkyd coating compositions may be used as protective coatings for farm equipment and as a finish or refinish for trucks and automobiles. They are also extensively employed in architectural varnishes and enamels which require high gloss. However, rising health and environmentally concerns over the emission of organic compounds from solvent-based paints have resulted in strict regulation of the amount of volatile organic compounds (VOC) emitted from applied paints. In addition, rapid advances in technical innovation require improvements in the properties of coatings compositions. For example, it is desired that pigments be dispersed more effectively with higher stability in order to produce coating finishes having improved gloss (i.e., gloss at 60°) and distinctiveness-of-image gloss (i.e., gloss at 20°). Moreover, these coatings often exhibit problems with adhesion, flexibility, and resistance to corrosion and chemicals.
In an attempt to comply with the challenges of increased regulation and improved performance, industry has devoted much effort toward developing water-borne and high solid alkyds coatings which employ far lower amounts of organic solvents than conventional coatings. In spite of these substantial efforts, a need exists in the industry for such improved water-borne alkyds and high solid alkyds coatings.
High solid alkyds which employ less organic solvent than conventional alkyds often suffer from a dramatic increase in viscosity as the amount of solvent employed decreases. It has often been necessary for a high solid system to use lower molecular weight resins in order to maintain a workable paint viscosity. However, such systems tend not to develop the same hardness and through-dry in thick films in the same amount of time when compared to systems using higher molecular weight materials. Moreover, the additional functionality (which may build up the coating molecular weight after application) usually required for such high solid systems commonly results in adverse performance and higher production costs. One example of the use of additional functionality is to increase the level of unsaturated fatty acid to ensure sufficient crosslinking to achieve acceptable coating properties. One of the major drawbacks in the use of such high solid alkyds is the development of severe yellowing in the cured coatings due to the increased level of unsaturated fatty acid. U.S. Pat. No. 5,370,939 references attempts to address this yellowing problem in alkyd coatings by via the incorporation of polyhydroxy based allyl ethers into alkyds to replace a part of, or all of, the fatty acid. In U.S. Pat. No. 4,591,518, alkyd resins containing pendant polymerizable unsaturated groups attached to the alkyd through urethane linkages are claimed to improve high solid performance.
Water-borne alkyds coatings which use water as a dispersing medium are mainly emulsions and water-dispersible resins. Although showing an impressive success in replacing organic solvent coatings in many applications, water-borne alkyd coatings have not been able to satisfy the need of the coating industry in many applications because of certain inherent problems (e.g., insufficient gloss, water sensitivity, hydrolytic stability, and the difficulty of controlling water evaporation after application).
Coating compositions of acrylic polymers commonly provide finishes with excellent appearance, weatherability and durability. Coatings compositions of alkyds are known for their excellent gloss and their ability to be cured at ambient temperature. However, such alkyd coating compositions are also known for their inferior weatherability and durability when compared to acrylic finishes. Tremendous efforts have, therefore, been concentrated on developing interpolymers which are the combination of acrylic polymer and alkyd polymer.
Simply blending acrylic polymers and alkyds does not provide an optimum finish, as these acrylic polymer and alkyds are generally not compatible.
In the art of emulsions utilizing alkyd resins, interpolymer emulsions of acrylic polymers and alkyds have been prepared typically by following either one of two different procedures. In one procedure, an alkyd resin and compatible vinyl emulsion are separately formed, and then admixed together. By the other procedure, vinylic monomers are in situ polymerized in the presence of a preformed solution or dispersion of alkyd resin so as to provide an interpolymer system. The in-situ polymerization can take place with or without a conventional emulsifier. An example of this is U.S. Pat. No. 4,116,903, where a neutralized, aqueous solution of alkyd resin is utilized as sloe emulsifier to stabilize the in-situ vinylic emulsion polymerization.
In U.S. Pat. No. 4,273,690, an interpolymer is produced by grafting alkyd resin to the acrylic polymer backbone through urethane moiety. A number of patents have described the production of water-borne alkyds via the use polyurethane dispersion (see U.S. Pat. No. 3,412,054 and European Patent Application No. EP 0017199A1). Polyurethane dispersions or isocyanate compounds (which are the precursor for urethane moiety) are quite costly, and result in much higher production costs for water-borne alkyds when compared to conventional solventborne alkyds.
The water-borne alkyds often exhibit poor hydrolytic stability, in that they often do not have the capability to withstand storage for long periods of time at the high storage temperatures often found in warehousing and manufacturing facilities. Hydrolysis of alkyds may result in the separation of the coatings composition into phrases, accompanied by the settling of solid materials to the bottom or substantial reductions in viscosity and the diminished performance of the coating materials. U.S. Pat. No. 5,096,959, attempts to improve the hydrolytic stability of water-borne alkyds by reacting the base alkyd commonly used for such compositions with a polybasic acid composition comprising one or more cycloaliphatic polycarboxylic acids. However, this approach requires the use of costly cycloaliphatic polycarboxylic acids, thereby increasing production costs.
An attempt to improve the adhesion property of water-borne alkyds is disclosed in U.S. Pat. No. 4,649,175, which teaches the incorporation of nitrogen-containing compounds into the alkyds. This incorporation, however, increases the cost of production of such water-borne alkyds.
Therefore, an object of this invention is to solve these major problems by disclosing rosin-fatty acid ester vinylic polymer compositions.
Another objective is to disclose rosin-fatty acid ester vinylic polymer emulsion compositions.
A further objective is to disclose rosin-fatty acid ester vinylic polymer compositions which exhibit properties that make them useful as support resins in water-based emulsions.
Another objective is to disclose rosin-fatty acid ester vinylic polymer emulsion compositions which exhibit properties that make them useful in formulating water-based inks, overprint, and other coating formulations.